Police has registered a case under the Protection of Children against Sexual Offences (POCSO) act.
A probationary sub-inspector was arrested in Kerala on Tuesday in connection with the alleged sexual assault of a minor girl at Mangalam town in the district over a six month period.
The accused, Laiju, was attached to Mararikulam police station, police said.
"With today's arrest, five persons, including two police personnel, have been nabbed in connection with the case," Alapuzha Deputy Superintendent of Police PV Baby, who has formed a Special Investigation Team to probe it, said.
Earlier, a senior civil police officer, Nelson Thomas, who was working with the Narcotics cell, was arrested from Bengaluru.
The girl's relative, a 24 year-old woman, who has also been arrested, is the first accused in the case.
Police said the woman had taken the 16-year-old girl, hailing from a poor family, to various hotels and lodges at night where she was allegedly sexually assaulted.
Following suspicion, neighbours near her home informed police and the woman was nabbed.
Two others Prince, 28, and Jinimon, 22, hailing from the same town where the girl belongs, have also been arrested, police said.
Police have registered a case against all five persons under the Protection of Children against Sexual Offences (POCSO) act.